U.S. patent number 4,234,230 [Application Number 06/056,595] was granted by the patent office on 1980-11-18 for in situ processing of mined oil shale.
This patent grant is currently assigned to The Superior Oil Company. Invention is credited to Bernard E. Weichman.
United States Patent |
4,234,230 |
Weichman |
November 18, 1980 |
In situ processing of mined oil shale
Abstract
A method for the recovery of products from nahcolite-bearing oil
shale ore deposits which comprises, in pertinent part, in situ
retorting of oil shale ore from which a major portion of the
nahcolite has been separated.
Inventors: |
Weichman; Bernard E. (Houston,
TX) |
Assignee: |
The Superior Oil Company
(Houston, TX)
|
Family
ID: |
22005458 |
Appl.
No.: |
06/056,595 |
Filed: |
July 11, 1979 |
Current U.S.
Class: |
299/2; 299/5 |
Current CPC
Class: |
E21B
43/28 (20130101); E21B 43/281 (20130101); E21B
43/243 (20130101); E21B 43/24 (20130101) |
Current International
Class: |
E21B
43/28 (20060101); E21B 43/16 (20060101); E21B
43/243 (20060101); E21B 43/24 (20060101); E21B
43/00 (20060101); E21C 041/10 () |
Field of
Search: |
;299/2,4,5 ;175/53
;208/11R ;423/119 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Attorney, Agent or Firm: Arnold, White & Durkee
Claims
What is claimed is:
1. A method of recovering products from a nahcolitebearing oil
shale ore deposit comprising the steps of:
(a) defining a retort zone within the deposit;
(b) mining the nahcolite-bearing oil shale ore from the retort
zone;
(c) crushing the mined oil shale ore to form particles comprising
substantially nahcolite and particles comprising substantially oil
shale;
(d) separating the substantially nacholite particles from the
substantially oil shale particles to recover a substantially
nahcolite product;
(e) restoring the oil shale particles to the retort zone; and
(f) retorting the oil shale particles to recover hydrocarbon
products.
2. The method of claim 1, wherein the separating of the
substantially nahcolite particles from the substantially oil shale
particles comprises screening the particles to produce a larger
sized fraction of substantially oil shale particles and a smaller
sized fraction of substantially nahcolite particles.
3. The method of claim 2 comprising the additional steps of:
(a) installing flow distribution piping in the retort zone; and
(b) sealing the retort zone prior to retorting.
4. The method of claim 3, wherein the step of restoring the
substantially oil shale particles to the retort zone comprises:
(a) segregating the oil shale particles into a plurality of size
groups; and
(b) progressively restoring the oil shale particles to the retort
zone according to size, the smallest size oil shale particles being
restored to the retorting zone first.
5. The method of claim 4, wherein the step of retorting comprises
combustion retorting.
6. The method of claim 5, wherein said combustion retorting
comprises:
(a) supplying natural gas and air to the top of the retort
zone;
(b) igniting said gas; and
(c) maintaining combustion in said oil shale particles in a moving
combustion front through the retort zone.
7. The method of claim 1, wherein said oil shale ore includes
dawsonite and said retorting comprises non-combustion heating to
recover hydrocarbon products and to convert said dawsonite to a
more soluble aluminum compound; and comprising the additional steps
of:
(a) caustic leaching of the retorted, spent shale to dissolve the
aluminum compound; and
(b) precipitating aluminum hydroxide from the caustic leach
liquor.
8. The method of claim 2, wherein at least about three-fourths of
the nahcolite is removed from the mined oil shale ore by screening
and is recovered in the smaller sized, substantially nahcolite
fraction.
9. The method of claim 1, wherein at least 60% of the nahcolite is
removed from the mined oil shale ore in the separation step.
10. A method of recovering hydrocarbon products, nahcolite, and
alumina from a nahcolite-bearing oil shale ore deposit which
includes dawsonite, comprising the steps of:
(a) mining the oil shale ore from and constructing a retorting zone
within said deposit, wherein said retorting zone comprises a room
substantially enclosed by a barrier pillar, and wherein said room
is supported by a plurality of pillars whose volume is
approximately 25% of the volume of said retorting zone;
(b) crushing said mined oil shale ore to produce fine nahcolite
particles and relatively coarser oil shale particles;
(c) screening the fine nahcolite particles from the coarser oil
shale particles to recover the nahcolite;
(d) sealing the retorting zone against entry of water;
(e) returning the coarser oil shale particles to the retorting
zone;
(f) retorting said oil shale in situ by heating to recover
hydrocarbon products and to convert the dawsonite to a more soluble
aluminum compound;
(g) leaching the spent shale with caustic to dissolve the aluminum
compound;
(h) precipitating aluminum hydroxide from the caustic leach liquor;
and
(i) calcining the aluminum hydroxide to recover alumina.
11. The method of claim 10 comprising the additional steps of:
(a) leaching the remaining nahcolite from said coarser oil shale
particles;
(b) filtering and evaporating the aqueous leach liquor to recover
sodium carbonate; and
(c) drying the oil shale particles prior to retorting.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the production of minerals from oil shale
deposits, and, more particularly, to recovery of nahcolite and
hydrocarbon products by in situ retorting of mined,
nahcolite-bearing oil shale ore from which a major portion of the
nahcolite has been separated.
2. Background of the Invention
Nahcolite is a naturally occurring sodium bicarbonate which is
sometimes found in substantial quantities in oil shale deposits. As
used herein, the terms "ore" and "oil shale ore" refer to such
nahcolite-bearing oil shale, and "oil shale" refers to the fraction
that remains after a major portion of the nahcolite has been
removed from the ore.
Deposits of oil shale ore have not been utilized to a significant
extent as an oil source due to the relatively high cost of mining
and recovering the oil, and the environmental considerations
involved in such an operation. Oil shale ore formations contain
hydrocarbons which exist in the form of kerogen. For all practical
purposes, kerogen is immobile within the shale. However, it is
well-known in the art that hydrocarbons can be recovered by heating
the oil shale in a process called retorting. Two basic techniques
have been utilized for this purpose: surface retorting and in situ
retorting.
In U.S. Pat. No. 3,821,353 to Weichman, there is disclosed a
process for recovering hydrocarbons, aluminum, sodium carbonate
and/or nahcolite from oil shale ore. Further, mechanical separation
of nahcolite from oil shale, leaching of nahcolite from oil shale,
and recovery of alumina and aluminum hydroxide from retorted oil
shale are disclosed. In particular, Weichman discloses two methods
of retorting, neither of which involves in situ retorting.
Methods of in situ retorting are well-known in the art. As the name
suggests, the retort chamber is formed in the oil shale deposit.
According to well-known procedures, the retort chamber may comprise
one or a plurality of rooms within a gallery. Rooms are formed by
removing a portion of the shale from the ore deposit by
conventional mining techniques such as room and pillar mining. The
surrounding shale is then rubblized by use of explosives, and the
rubblized shale is then retorted by in situ combustion or by
heating gases externally and passing them through the rubblized
bed. With either technique, the hydrocarbons produced are recovered
at the lower end of the retort.
In particular, U.S. Pat. No. 3,950,029 to Timmins and 3,957,305 to
Peterson describe in situ retorting of oil shale. In the '029
patent, a method of in situ retorting is described wherein a
retorting zone is formed in the deposit and the zone comprises at
least two galleries separated by a barrier wall which is
sufficiently thick to prevent leakage of gas between galleries.
Each gallery comprises a plurality of rooms having walls
substantially thinner than the barrier wall between galleries. The
rooms are constructed by conventional mining techniques of removing
a portion of the shale within the defined room and rubblizing the
surrounding shale by use of explosives or other suitable
techniques. Timmins suggests that one gallery can then be retorted
while work continues in an adjoining gallery.
The '305 patent discloses formation of the in situ retort chambers
by means of a side excavating machine. A major portion of the
excavated shale is deposited in the chambers. Once excavation is
completed and the retort chambers are suitably sealed, the chambers
formed according to the above description are then retorted.
In situ retorting reduces the problems of cooling and disposing of
the spent shale inherent in surface retorting; however, the known
and above-described in situ methods likewise have inherent problems
which must be considered in making an in situ operation
commercially feasible.
Present methods of in situ retorting do not provide for recovery of
minerals other than hydrocarbons and, in the instance of
hydrocarbon recovery, provisions could be made for more economical,
efficient recovery.
In particular, the present methods of retorting which utilize
explosives to rubblize the shale have many problems. With blasting
it is difficult to control the size distribution of the oil shale
ore particles in the retort volume. Many large boulders that result
from the blast do not fully retort. Also, the smaller particules,
i.e., the "fines," produced by the blast tend to produce areas of
low permeability in the retort. Since the burning front in the
retorting zone advances more rapidly in the more permeable zones,
"channelling" of flow can result during the retorting operation,
which can result in substantial quantities of oil shale ore not
being fully retorted. Inefficiency and environmental damage also
may result from those processes where the in situ retort is not
fully sealed. For example, water can leak into the retort during
burning, causing great heat loss, and ground water can be
contaminated. Finally, methods currently employed for separating
nahcolite from oil shale ore can create nahcolite particles which
can be carried away by winds resulting in environmentally
undesirable dust.
SUMMARY OF THE INVENTION
A significant feature of the method of the present invention
comprises the in situ retorting of nahcolite-bearing oil shale ore
from which a major portion of the nahcolite has been separated. Yet
another significant feature of the present invention comprises the
prevention of channeling during retorting by removal of relatively
small particles, i.e. the "fines," from the oil shale which is
retorted. These features permit the economic, efficient, and
environmentally sound recovery of nahcolite and shale oil from
nahcolite-bearing oil shale ore deposits.
In accordance with one embodiment of the method of this invention,
oil shale ore is extracted from a retort zone and subjected to
underground impact crushing. This step produces relatively "coarse"
particles and relatively "fine" particles. Since nahcolite is more
brittle than oil shale, a majority of the relatively "fine"
particles are nahcolite, while a majority of the relatively
"coarse" particles are oil shale. The finer particles are separated
by size from the coarser oil shale particles, such as by screening,
and the coarser particles are then returned to the original mined
out chamber which forms the in situ retort, from which hydrocarbons
are recovered. The finer particles, comprising substantially
nahcolite, are then brought to the surface as product.
In accordance with another feature of this invention, the oil shale
particles are grouped by size and the smallest oil shale particles
are placed on the floor of the in situ retort and progressively
larger oil shale particles are stacked on top. Before retorting,
the retort may be sealed and, thereafter, hydrocarbons can be
recovered during retorting of the shale.
Another feature of the invention includes the further separation of
nahcolite from the oil shale to be retorted by leaching the
nahcolite from the coarse oil shale particles and recovering sodium
carbonate by evaporating the aqueous leach liquor. The oil shale
ore subjected to this leaching step can then be efficiently
retorted to recover hydrocarbon products.
The in situ recovery of products is environmentally advantageous
for many reasons. In particular, the nahcolite recovered in situ
may be used for air pollution control and its recovery in situ
reduces generation of dust particles which damage the environment.
Further, in situ retorting obviates spent shale disposal problems.
Still further, efficient in situ retorting results in conservation
of fuel. Other environmental advantages will become apparent to
those skilled in this art from a reading of the complete
specification.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing:
FIG. 1 is a block flow diagram which shows the sequence of steps
according to one embodiment of the method of the present
invention.
DESCRIPTION OF SPECIFIC EMBODIMENT
It will be appreciated that the method of the present invention may
have many embodiments. One embodiment of the method is described to
give an understanding of the invention. It is not intended that the
description herein should limit the true scope and spirit of the
invention.
Referring to FIG. 1, the method of the present invention first
comprises the step 100 of mining a portion of the oil shale ore
from the retort zone. Step 100 may be accomplished with
conventional techniques, e.g., the room and pillar method.
The next step in accordance with the present invention is to
subject the mined oil shale ore to impact crushing (step 101),
which produces particles of various sizes. Since the nahcolite is
more brittle than the oil shale, the smaller, i.e., "finer"
particles comprise substantially nacholite, while the larger, i.e.
"coarser," particles comprise substantially oil shale.
The next step 102 of the method according to the present invention
is to separate the crushed particles by size to remove the smaller
nahcolite particles from the coarser oil shale particles. This step
results in the separation of a substantial portion of the nahcolite
from the oil shale. In situ separation of nahcolite eliminates dust
hazards which may be created when this operation is conducted on
the surface. This separation step may be carried out by one or more
sequential impact crushing steps followed by screening, or by a
series of impact crushing and screening steps. In either event,
during screening, particles of a size less than about 35 mesh are
separated from the large particles. In one embodiment, the smaller
particles are then conveyed to the surface, as shown
diagrammatically by step 110. Although the smaller particles
screened out are substantially nahcolite, they may contain as much
as about 20-30 percent oil shale. This material may be sold "as is"
for air pollution control, e.g., cleaning flue gases and the like.
In particular, this material may be used as a scrubbing agent for
the removal of oxides of sulfur, nitrogen, and other elements from
flue gas. Alternatively, the fines may be subjected to a water
leach, filtration, and calcining of the filtered leach liquor to
recover pure sodium carbonate.
The next step 103 of the present method is to restore the remaining
coarser oil shale particles, from which about 60 to about 80
percent of the nahcolite has been removed, to the retort zone. In a
preferred embodiment, step 103 comprises selectively grouping the
oil shale particles according to size. This grouping may be
accomplished by sequential screening of the particles through
screens of different mesh sizes, or by any other appropriate method
of separation, such as optical sorting. The smallest particles are
placed on the floor of the retort zone, with progressively larger
particles being placed on top.
The purpose of this particular stacking arrangement is two-fold; it
allows for good distribution of flow with a minimum of channelling,
and it allows for retorting to terminate after the larger particles
are completely retorted. This latter phenomenon occurs because the
smaller particles on the bottom (gas-exit side of the retort)
require less heat to completely retort, and, accordingly, the
retorting operation is terminated when the larger particles at the
top are completely retorted. Appropriate piping may be laid or
installed across the top or above the bed of oil shale to be
retorted, to insure good flow distribution of hot gas or of natural
gas and air for combustion retorting, through the retort zone.
Before retorting, all entrances into the retort zone should be
sealed. The seals can be formed by pouring grout, for example
concrete, into a suitable form.
Hydrocarbons may be recovered from the oil shale by subjecting it
to heat, i.e. retorting it, as shown in step 104. Although other
products may be recovered from the oil shale if heat is applied in
a controlled manner and the temperature does not exceed a certain
maximum, as set forth in U.S. Pat. No. 3,821,353, combustion
retorting is the preferred method for underground or in situ
retorting in the absence of a substantial aluminum content in the
ore. This is accomplished by initially supplying natural gas or the
like to the top of the retort bed, igniting it, and maintaining
combustion in the bed in a downwardly-moving combustion front
through the retort. It should be understood that the particular
arrangement of the oil shale particles comprising the retort bed
and the use of distribution pipes where appropriate will allow for
the even distribution of gas flow through the retorted bed.
As the heat front generated by the combustion passes through the
retort bed, pyrolysis occurs and hydrocarbons are driven from the
shale. These hydrocarbons may condense on the relatively cooler
shale particles below, and eventually are recovered at the bottom
of the retort, as indicated in step 105. Preferably, this
collection is made in a sump which has been formed at or near the
bottom of the retort. The collected hydrocarbons may then be pumped
to the surface and further processed or treated as described in
U.S. Pat. No. 3,821,353. It should be understood that a portion of
the hydrocarbons also may be recovered from the oil shale ore which
forms the support pillars and the barriers, and from other
surrounding oil shale ore exposed to the heat.
It will be appreciated that when hot gas retorting is used, the
temperature at which the retorting operation is carried out may be
controlled with greater precision than when combustion retorting is
used. For reasons set forth more specifically in U.S. Pat. No.
3,821,353, the optimum retort temperature may be as high as
550.degree. C. to 600.degree. C., but preferably is controlled at
about 475.degree. C. if it is desired to maximize recovery of
aluminum values from the retorted shale. This optimum temperature
may vary according to the composition of the oil shale ore to be
retorted, and the higher temperatures of combustion retorting can
be utilized if alumina is not to be recovered.
After retorting at controlled temperature, the spent shale may be
subjected to a caustic leach in order to recover aluminum
hydroxide. It should be understood that the hydrocarbons and
nahcolite recovered in the practice of this invention may be
further processed to produce other related products. For example,
the nahcolite recovered during the screening step may be subjected
to a water leach, and the leach liquor filtered and then calcined
to produce sodium carbonate. The sodium carbonate may be used in
the make up of the caustic leach. Again, a more detailed
description of these processes may be found in U.S. Pat. No.
3,821,353.
The description of the foregoing particular and preferred
embodiments is not intended to limit the scope of this invention.
Various modifications of the disclosed embodiments, as well as
other embodiments of the invention, may be apparent to persons
skilled in the art upon reference to this description. For example,
the step of separating the crushed ore particles to obtain a
substantially nahcolite fraction and a substntially oil shale
fraction may be accomplished by optical sorting. It is therefore
contemplated that the appended claims will cover any such
modifications or embodiments as fall within the true scope of the
invention.
* * * * *